For decades sceptics have dismissed talk of the female G spot as a sort of gynaecological UFO – much searched for, much discussed, but unverified by objective means.

Now scientists believe they have finally obtained the first evidence of its existence – but only in some lucky women.

The G spot is said to confer the capacity for orgasms on its fortunate possessers. Many writers suggested it was a small hypersensitive area of the vagina about three quarters of the way up the anterior wall.

Italian researchers, who used ultrasound scans to explore inside the vaginas of 20 women, say they have found a thickened area of tissue in those who said they had experienced vaginal orgasms – but not in those who had not.

“For the first time it is possible to determine by a simple, rapid and inexpensive method if a woman has a G spot or not,” Emmanuele Jannini, from the University of L’Aquila, told New Scientist.

The finding is unlikely to settle the issue. Other researchers queued up to offer their interpretations of the results, suggesting the thickened tissue could be the internal part of the clitoris, or that those who had learnt to experience orgasms through practice had altered their anatomy.

Dr Jannini plans larger studies to help women decide whether to give up the hunt – or tell their partners to try harder.